Thermostable lipoprotein lipase, process for producing the same, and triglyceride determining reagent using the same

ABSTRACT

The present invention is directed toward a thermostable lipoprotein lipase capable of hydrolyzing triglycerides in lipoproteins to glycerol and fatty acids, a process for producing the thermostable lipoprotein lipase, and a blood triglyceride determining reagent containing the thermostable lipoprotein lipase. The thermostable lipoprotein lipase exhibits about 100% retention of the hydrolyzing activity when treated in a buffer having a pH of from about 4 to 7 at about 60° C. for about 15 minutes and a glycerol forming activity/fatty acid forming activity ratio of at least about 15%. The process comprises cultivating a thermophilic actinomycetes, particularly Streptomyces 7825 (FERM P-9983, FERM BP-2489 and recovering lipoprotein lipase from the culture.

FIELD OF THE INVENTION

This invention relates to a lipoprotein lipase having excellentthermostability and high glycerol formation activity, a process forpreparing the same, and a reagent containing the same which is usefulfor quantitative determination of triglycerides.

BACKGROUND OF THE INVENTION

The existence of lipoprotein lipase (hereinafter referred to an "LPL")as a clearing factor was recognized in 1943 by P. F. Hahn through hisstudy on the circulatory amount of red blood cells. P. F. Hahn foundthat the injection of heparin to an alimentary lipemic dog results inclearing of the milky plasma. Thereafter, it was elucidated that theclearing mechanism is due to the hydrolysis of lipoprotein with LPL. LPLhad been detected in the tissues of various animals. Thus, LPL plays animportant role in lipid metabolism in animals.

Arima et al, Agr. Biol. Chem., Vol. 30, p. 515 (1966) reported that anenzyme similar to LPL of animal origin exists in microorganisms and thisenzyme has been called microbial LPL. Because the microbial LPL can beproduced in large quantity, studies on the utilization of microbial LPLhave been promoted. In particular, applications regarding thequantitative determination of triglycerides in blood have beendeveloped.

Microorganisms capable of producing LPL include various genera such asPseudomonas, Mucor, Streptomyces, Serratia, Aeromonnas, Bacillus (seeAgr. Biol. Chem., Vol. 31, p. 924 (1967), JP-B-41-7836, andJP-B-58-37835 (the term "JP-B" as used herein means an "examinedpublished Japanese patent application"), and Rhizopus (see Agr. Biol.Chem., Vol. 43, p. 2125 (1979), and JP-B-58-37834). However, since allof these microorganisms are mesophiles, LPL produced therefrom exhibitspoor stability.

With the recently increasing use of enzyme assays in clinicalexaminations, the unstability of enzymes has given rise to greatproblems. Techniques for obtaining thermostable enzymes fromthermophilic microorganisms, have been developed to improve enzymestability.

However, thermostable LPL has not yet been developed and has thus beenkeenly demanded.

Further, in cases when LPL is used in the quantitative determination oftriglycerides in blood, LPL must exhibit high activity to form glycerolso as to reduce the requisite amount of the reagent used and to shortenthe reaction time required. Thus, the use of any known LPL is notsatisfactory.

It is known that lipases inclusive of LPL exhibit specificity to thethree ester linkages of a triglyceride substrate. In the quantitativedetermination of blood triglyceride using LPL, glycerol formed byhydrolysis is preferably introduced into a detection system by acoupling enzyme. In order to form glycerol in an amount proportional tothe triglyceride amount, it is preferable to use an LPL capable ofhydrolyzing the three ester linkages without showing selectivity. Thepositional specificity of known LPL to ester linkages, being expressedin a percentage of glycerol formation activity to fatty acid formationactivity, is generally low. The highest of the cases reported so far, is1.97% of LPL originating in a microorganism belonging to the genusPseudomonas as described in JP-A-59-187780 (the term "JP-A" as usedherein means an "unexamined published Japanese patent application").

SUMMARY OF THE INVENTION

One object of this invention is to provide an LPL having excellentthermostability and high glycerol formation activity.

Another object of this invention is to provide a process for producingsuch an LPL.

A further object of this invention is to provide a triglyceridedetermining reagent containing such an LPL.

The inventors have searched extensively for microorganisms capable ofproducing the above-described LPL. As a result, it has now been foundthat a thermophilic actinomycetes (Streptomyces 7825 (FERM P-9983, FERMBP-2489) isolated from the soil of Izu Atagawa, Shizuoka, Japan iscapable of producing LPL having the above-described properties.

That is, the present invention relates to a thermostable LPL able tohydrolyze triglycerides in lipoprotein to glycerol and fatty acids. TheLPL, after treatment in a buffer having a pH of from about 4 to 7 at atemperature of about 60° C. for about 15 minutes, retains about 100% ofits hydrolyzing activity, and the glycerol forming activity of which isat least about 15% of the fatty acid forming activity.

The present invention further relates to a process for producingthermostable LPL which comprises cultivating a thermophilicactinomycetes and recovering thermostable LPL from the culture.

The present invention furthermore relates to a reagent containing LPLfor the quantitative determination of triglycerides in body fluids,wherein said LPL has an activity to hydrolyze triglycerides inlipoproteins to glycerol and fatty acids, said hydrolyzing activitybeing about 100% retained after treatment in a buffer at a temperatureof about 60° C. for about 15 minutes, and the ratio of glycerol formingactivity to fatty acid forming activity being at least about 15%.

The LPL according to the present invention is superior to conventionallyknown LPL's in thermostability and in the ratio of glycerol formationactivity to fatty acid formation activity. Therefore, when used as atest reagent, the LPL makes it possible to considerably extend the lifetime of the reagent while reducing a time required for determination persample, thus greatly contributing to the industry.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing the optimum pH of the LPL of the presentinvention.

FIG. 2 is a graph showing pH stability of the LPL of the presentinvention.

FIG. 3 is a graph showing the optimum temperature of the LPL of thepresent invention.

FIG. 4 is a graph showing heat stability of the LPL of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The hydrolysing activity of the present LPL is retained at a retentionof about 100% when it is treated in a buffer at about 60° C. for about15 minutes. The concentration and pH of the buffer herein referred toare not particularly limited but, usually, the concentration ranges fromabout 5 to 500 mM, preferably about 10 to 250 mM, more preferably about20 to 100 mM, and the pH ranges from about 4 to 7, preferably about 4.5to 6, more preferably about 5. It is particularly preferable to use anacetic acid buffer (pH=5.0).

The LPL of the present invention produced by Streptomyces 7825 (FERMP-9983, FERM BP-2489) has the following physiochemical properties:

(a) Action

It acts on triglycerides of lipoproteins to hydrolyze them into glyceroland fatty acids. The lipoproteins include not only artificiallipoproteins but human blood lipoproteins.

(b) Substrate Specificity

It exhibits activity on lipoproteins consisted of various triglyceridesas shown in Table 1 below. In Table 1, the activity is expressedrelative to an olive oil as a standard (100%).

                  TABLE 1                                                         ______________________________________                                        Substrate Specificity                                                                       Relative Activity                                               Triglyceride  (%)                                                             ______________________________________                                        Triacetin     28                                                              Tributyrin    22                                                              Tricaproin    46                                                              Tricaprylin   148                                                             Tricaprin     153                                                             Trilaurin     234                                                             Tripalmitin   99                                                              Tristearin    29                                                              Triolein      75                                                              Olive oil     100                                                             ______________________________________                                         (c) Optimum pH: 8.0 to 9.0 as Shown in FIG. 1

Stable pH: 4.0 to 7.0 (when treated at 60°, 30 mins.) as shown in FIG.2.

(d) Optimum Acting Temperature:

50° to 60° C. as shown in FIG. 3.

(e) Heat Stability

About 100% of the activity can be retained after treatment in 50 mMacetate buffer (pH 5.0) at about 60° C. for about 15 minutes as shown inFIG. 4.

(f) Inhibition

It is 30 to 40% inhibited by Zn²⁺, Fe³⁺, and Mg²⁺ each at aconcentration of 1 mM, about 40% inhibited by 3M NaCl, about 40%inhibited by 10 mM deoxycholic acid, or about 30% inhibited by 400 μg/mlprotamine sulfate.

(g) Molecular Weight

30,000 to 50,000 (gel-filtration)

(h) Titer

Titer determination is principally based on the quantitativedetermination of glycerol formed through the action of LPL on artificiallipoprotein prepared from olive oil as described in Clin. Chim. Acta.,Vol. 22, p. 393 (1968).

Reagent

A mixture of 5 g of olive oil and 5 ml of a 5% (v/v) Triton X-100solution is subjected to ultrasonication for 10 minutes to prepare asubstrate emulsion.

12 ml of 25 mM metaperiodic acid and 20 ml of isopropanol are mixed. 1Nacetic acid is added thereto to make 100 ml.

2,4-Pentanedione (0.75 ml) and 2.5 ml of isopropanol are mixed, and 2Mammonium acetate is added thereto to make 100 ml.

Procedure

Seventy microliters of the abovementioned substrate solution, 20 μl of a0.5M glycine buffer (pH 8.5), 50 μl of 10% (w/v) BSA, and 55 μl of waterare mixed in a test tube, and the system is preheated at 37° C. 5 μl ofan enzyme solution having an enzyme concentration adjusted to about 10U/ml, is added to the system. The system is then allowed to react at 37°C. for 10 minutes. After completion of the reaction, the test tube issoaked in boiling water to stop the reaction. After allowing the testtube to cool, 400 μl of isopropanol is added to the reaction system,followed by stirring. The mixture is then centrifuged. 2 ml ofisopropanol is then added to 100 μl of the supernatant liquor. Thesolution is mixed with 1 ml of the above prepared metaperiodic acidsolution and 0.5 ml of the above prepared acetylacetone solution toeffect a reaction at 50° C. for 30 minutes. The absorbance of the systemat 405 nm is measured. A blank estimation (control) is run on a systemcontaining no enzyme solution.

From the measured values, a calibration curve is prepared using aglycerol solution having a known concentration. Thus the glycerolcontent of the reaction mixture is determined using the preparedcalibration curve.

The enzyme activity is expressed by taking the amount of the enzymewhich forms 1 μmol of glycerol per minute as 1 U.

(i) Ratio of Glycerol Formation Activity

The glycerol formation activity of the LPL is at least about 15% of thefatty acid formation activity. While activity is generally expressed interms of glycerol formation activity as stated above, it is necessary toobtain the fatty acid formation activity before the ratio of glycerolformation activity to fatty acid formation activity can be obtained. Thefatty acid formation activity can be determined by assaying anisopropanol extract obtained in the same manner as described above forthe formed fatty acid content by the use of a commercially available kitfor determining free fatty acids (e.g., NEFAC-Test produced by Wako PureChemical Industries, Ltd.), taking the amount of the enzyme capable offorming 1 μ equivalent of fatty acids per minute as 1 U.

Accordingly, the ratio of glycerol formation activity to fatty acidformation activity can be calculated from formula: ##EQU1##

(j) Purification Method

As hereinafter described.

(k) Crystal Structure and Elementary Analysis

Unconfirmed

The LPL according to the present invention can be produced bycultivating a thermophilic actinomycetes and recovering the produced andaccumulated LPL from the culture.

The thermophilic actinomycetes for use in the present invention is notlimited as long as it is capable of producing the LPL of the invention.One example of such a microorganism is Streptomyces 7825 isolated fromthe soil. The microbiological properties of this strain are describedbelow.

The experiments for the determination of the microbiological propertieswere in accordance with the methods described in Nippon HosenkinKenkyukai (ed.), Hosenkin no Dotei Jikkenho (Identification Test Methodof Actinomycetes), (1975) and Kazuo Komagata (ed.), Biseibutsu no KagakuBunrui Jikkenho (Chemical Classification Test Method of Microorganisms)(1982).

(a) Morphology

The culture after cultivation by slide cell culture in a nutrient agarmedium at 50° C. for 4 days was observed under a microscope and ascanning electron microscope.

Branching of sporulating hypha: simple branching

Form of sporulating hypha: curved and spiral

Number of spores: 10 or more

Surface structure and size of spore: smooth, 0.5 to 1.0 μm×1.0 to 1.5 μmin diameter

Flagellospore: none

Sporangium: none

Growth position of sporephore: on aerial hyphae

Sclerotium formation: none

(b) Growth State in Various Media (on culturing at 50° C. for 6 days)

(1) Sucrose-nitrate-agar medium:

Spreading and flat milky colonies with thin

powderous brown aerial hyphae.

(2) Glucose-asparagine-agar medium:

Spreading and flat milky colonies with no aerial hyphae

(3) Glycerin-asparagine-agar medium:

Spreading and flat milky colonies with no aerial hyphae

(4) Starch-agar medium:

Spreading and flat milky colonies with abundant powderous brown aerialhyphae

(5) Tyrosine-agar medium:

Spreading and swollen milky colonies with thin powderous white aerialhyphae, brown pigment formed in the surrounding agar

(6) Nutrient agar medium:

Spreading and swollen milky colonies with abundant powderous gray aerialhyphae

(7) Yeast-malt-agar medium:

Spreading and wrinkled milky colonies with abundant powderous grayaerial hyphae

(8) Oatmeal-agar medium:

Spreading and flat milky colonies with no aerial hyphae

(c) Physiological Properties

(1) Growth temperature range: 2° to 55° C.

(2) Liquefaction of gelatin: +

(3) Hydrolysis of starch: +

(4) Coagulation and peptonization of skim milk: -

(5) Formation of melanin-like pigment: +

(d) Carbon Source Assimilability

(1) L-Arabinose: ±

(2) D-Xylose: ++

(3) D-Glucose: ++

(4) D-Fructose: ++

(5) Sucrose:

(6) Inositol: ++

(7) L-Rhamnose:

(8) Raffinose:

(9) D-Mannitol: ++

++: Strongly assimilative. Equal to or higher than glucoseassimilability

±: Doubtful. Slightly higher than control but much lower than glucoseassimilability.

: Non-assimilative. Equal to control and greatly lower than glucoseassimilability.

(e) Chemical Composition of Cell Wall: Cell Wall Type I

As a result of studying the above-described microbiological propertiesin accordance with Bergey's Manual of Determinative Bacteriology, 8thEd., this strain was identified to belong to the genus Streptomyces. Asa result of further research, the strain was found nearly consistentwith Streptomyces galbus in terms of spore color, form of sporephore,surface structure of spore, production of melanin-like pigment, andcarbon source assimilability, except for differences in L-arabinoseassimilability and color of the hyphae. Thus, the strain was judged tobe similar to but not the same as Streptomyces galbus. The strain wasdesignated as Streptomyces 7825 and deposited in the Agency ofFermentation Research Institute, 1,3, Higashi, Ichome, Tsukulog-Shi,Ibaraki-ken, 305, Japan (FERM P-9983, FERM BP-2489).

This strain is capable of producing the present LPL by culturing in anappropriate liquid nutrient medium containing an inducer. Aftercompletion of the cultivation, the culture filtrate is collected andpurified through various known methods as described, for example, inMethod in Enzymology, vol. 22, edited by W. B. Jakoby, Academic press(1971) to obtain the LPL of the present invention.

In more detail, since LPL synthesis by the strain is induced, theaddition of an inducer to the medium is desirable. Suitable inducersinclude fats and oils and fatty acids. The fats and oils include animaloils, e.g., lard, butter, fish oil, and whale oil; and vegetable oils,e.g., olive oil, soybean oil, rice bran oil, cotton seed oil, and sesamioil. The fatty acids include oleic acid, palmitic acid, and linolenicacid. The amount of the inducer to be added is not particularly limitedbut preferably ranges from about 0.1 to 3% (w/v). The medium furthercomprises carbon sources, nitrogen sources and inorganic salts generallyemployed for the cultivation of actinomycetes. Suitable carbon sourcesinclude glucose, glycerol, and soluble starch. Suitable nitrogen sourcesinclude peptone, urea, ammonium sulfate, corn steep liquor, defattedsoybean flour, yeast extract, and meat extract. Suitable inorganic saltsinclude monopotassium hydrogenphosphate, disodium hydrogenphosphate, andmagnesium sulfate. To accelerate the secretion of LPL into the medium,the addition of a surface active agent is effective. In particular, itis preferable to add about 0.05 to 0.5% (w/v) of a nonionic surfaceactive agent, e.g., Tween 40, Tween 60, or Tween 80. The medium isadjusted to a pH range of from about 6.0 to 7.5 in the vicinity ofneutrality. Aerobic conditions, such as stirring under aeration, producesatisfactory results. The cultivation temperature usually ranges fromabout 30° to about 50° C., and preferably around 50° C. to reduceculturing time. Culturing for from about 1 to 6 days, preferably fromabout 3 to 5 days under these conditions results in the accumulation ofa considerable quantity of LPL in the medium.

After completion of the cultivation, the mycelium pellets are removedfrom the culture, for example, by centrifugation or filtration tocollect a liquid. Purification of the enzyme ca be conducted by knownpurification procedures, such as salting-out with ammonium sulfate ororganic solvent precipitation with acetone, alcohols, etc. to obtain acrude enzyme. The crude product can further be purified to a higherdegree by various known chromatographic techniques, such as ion exchangechromatography, gel-filtration chromatography, and hydrophobicchromatography. Since the LPL of the present invention is stronglyhydrophobic, hydrophobic chromatography is preferably applied to obtaina highly purified enzyme.

Since the LPL according to the present invention is very heat stable, itcan be preserved for an extended period of time as compared toconventionally available LPL preparations. Thus, use of the present LPLis greatly advantageous.

For example, it is well known that LPL is useful as a reagent for theenzymatic assay of blood triglycerides. The assay is based on theprinciple that triglycerides in blood are hydrolyzed with LPL and theformed glycerol is quantitatively determined by enzymatic assay. Thequantitative determination of glycerol can be carried out by methodsutilizing glycerol kinase, glycerol dehydrogenase, and glycerol oxidase.The method utilizing is glycerol kinase commonly employed. According tothe method utilizing glycerol kinase, three kinds of enzymes; glycerolkinase glycerol-3-phosphate oxidase, and peroxidase, are employed. Eachof these enzymes, not limited in maker or origin, is used inconcentrations of from about 1.0 to 2.5 U/ml in a determining reagent.The buffer to be used is not particularly limited, but a weakly acidicbuffer such as citrate, β,β'-dimethylglutarate, acetate, succinate,futarate, phosphate or MES buffer is, preferably used. A suitable rangeof pH and concentration of the buffer is from about 5 to 7 and fromabout 10 to 100 mM, respectively. The reagent further contains ATPNa₂.3H₂ O and MgCl₂.6H₂ O which are necessary for the glycerol kinasereaction, in an amount of from 20 to 30 mg and from 3 to 50 mg,respectively, per 200 ml of the reagent. The reagent furthermorecontains 4-aminoantipyrine and a color former in the range of from about1 to 20 mg and from about 5 to 100 mg, respectively, per 200 ml of thereagent. The color former can be selected arbitrarily from phenolderivatives, aniline derivatives and toluidine derivatives such asp-hydroxydiphenyl, hydroquinone, hydroquinone monomethylether,cathechol, resorcinol, pyrogallol, o-phenylenediamine,m-phenylenediamine, aniline, diethylaniline, p-aminobenzoic acid,reductone and dimethyltoluidine. In order to increase solubility of thecolor formed, a surface active agent, e.g., Triton X-100, Span 20,sodium cholate, sodium dodecyl sulfate or dimethylbenzyl-alkyl-ammoniumchloride, is preferably added. These surface active agents may be usedin a concentration of about 1 to 10% (w/v) and an amount of about 2 to10 ml, preferably a concentration of about 2 to 6% (w/v) and an amountof about 3 to 6 ml, per 200 ml of the reagent.

To 1 ml of the thus prepared determining reagent are added severalmicroliters, preferably about 1 to 30 μl, more preferably 2 to 20 μl,most preferably 5 to 15 μl, of non-diluted serum, and severalmicroliters of the LPL (5 to 10 U/ml) according to the present inventionare then added thereto. The system is incubated in a cuvette whereby thecolor former develops a color in proportion to the amount oftriglycerides in the serum. The color formation is determined in termsof absorbance to quantitatively determine the amount of triglyceride inthe sample.

The present invention is now illustrated in greater detail by way of thefollowing Examples, but it should be understood that the presentinvention is not deemed to be limited thereto.

EXAMPLE 1

A medium (100 ml) comprising 0.5% of peptone, 0.1% of KH₂ PO₄, 0.1% ofNa₂ HPO₄.12H₂ O, 0.05% of MgSO₄.7H₂ O, 0.03% of yeast extract, 0.2% ofolive oil, and 0.5% of Tween 40 (pH 7.0) were placed in a 500 ml volumeErlenmeyer flask and autoclaved at 121° C. for 15 minutes.

Separately, Streptomyces 7825 (FERM P-9983, FERM BP-2489) was culturedin a test tube containing 5 ml of the medium having the same compositionas described above.

The culture liquid was inoculated into the above prepared medium andcultivated by rotary shaking culture at 50° C. for 3 days to obtain aseed culture for jar fermentation. 2 l of the same medium was chargedinto a 3 l-volume jar fermenter and autoclaved at 121° C. for 15minutes. 100 ml of the seed culture was then inoculated thereto,followed by culturing at 50° C. under aeration of 1 VVM and stirring at400 rpm.

After three days, the culture liquid was assayed for enzyme activity andfound to contain 0.2 U/ml of LPL. The culturing was ended at this point,and the mycelium pellets were removed by filtration to recover theculture filtrate.

The culture filtrate was passed through a column (4.4 cm in diameter; 10cm in height) packed with phenyl Sepharose pre equilibrated with a 25 mMphosphate buffer (pH 7.0). After the column was thoroughly washed withthe same buffer, the buffer was changed to 25 mM phosphate buffercontaining 1% Triton X-100 then LPL was eluted out showing a sharpelution peak The active fractions were collected, concentrated, andpassed through a column (2.2 cm in diameter, 90 cm in height) packedwith Sephadex G-75 pre equilibrated with a buffer containing 0.1% TritonX-100. The protein peak and the activity peak were consistent with eachother. SDS-polyacrylamide gel electrophoresis of the active fractionsgave a single band.

The resulting enzyme sample had a specific activity of 1.2 U/mg.

The amount of protein was quantitatively determined by Wang-Smith method(Anal. Biochem., Vol. 63, p. 414 (1975)).

Upon examination of the resulting purified enzyme, the aforesaidphysiochemical characteristics were confirmed. In particular, it wasproved that the present LPL is superior in thermostability to othercommercially available LPL's of microorganism origin. More specifically,when LPL's of Pseudomonas origin (product of TOYOBO Ltd.) or LPL's ofAlcaliqenes origin (product of Meito Sangyo Co., Ltd.) were treated at60° C. for 15 minutes at the pH at which the respective LPL's were moststable, i.e., 7.0 or 8.0, respectively, the retention of activity wasabout 70% or about 0%, respectively. The LPL of the present inventionthus obtained showed an activity retention of approximately 100% whensimilarly treated at a pH of 5.0. The LPL of the present invention ismost stable at a pH of 5.0.

The ratio of glycerol formation activity to fatty acid formationactivity of the LPL of the present invention was found to be 16%, whichis far higher than 1.97% attained by the LPL of Pseudomonas origin(product of TOYOBO Ltd.).

EXAMPLE 2

Blood triglyceride was determined using the reagent prepared from theLPL prepared in Example 1. The determination was carried out byhydrolyzing blood triglycerides with the LPL and assaying the formedglycerol with a coupling enzyme system comprising glycerol kinase,glycerol-3-phosphate oxidase, and peroxidase.

    ______________________________________                                        Glycerol Color Forming Solution:                                              ______________________________________                                        5% Triton X-100         4 ml                                                  N,N-Diethyl-m-toluidine                                                                               40 μl                                              4-Aminoantipyrine       4 mg                                                  ATP Na.sub.2.3H.sub.2 O                                                                               25 mg                                                 MgCl.sub.2.6H.sub.2 O   40 mg                                                 Glycerol kinase        200 U                                                  Glycerol-3-phosphate oxidase                                                                         500 U                                                  Peroxidase             300                                                                           purpurogallin U                                        ______________________________________                                    

The above-described glycerol color forming solution was dissolved in a50 mM MES buffer (pH 6.5) to make 200 ml. 10 μl of serum was added to 1ml of the resulting solution, followed by pre-incubation at 37° C. for 3minutes. The absorbance at 545 nm was read. Then 5 μl of the LPLobtained in Example 1 (adjusted to a concentration of 5 to 10 U/ml) wasadded thereto, followed by incubation at 37° C. The absorbance at 545 nmwas measured.

Ten minutes later, where the absorbance had reached a constant level, anincrease of absorbance (ΔA545) was obtained, and the triglyceridecontent was calculated therefrom according to equation: ##EQU2## whereinΔA545 is an increase of absorbance at 545 nm; 28.2 is a molecularextinction coefficient of the dyestuff (l/mmol/cm); 0.5 is a factorderived from the fact that 1 molecule of H₂ O₂ forms 1/2 molecule of thedyestuff; 1 is a light pass length (cm); and 885.45 is the molecularweight of triolein.

For reference, triglyceride determinations were run with theabove-described reagent on two kinds of commercially availablecontrolled serum preparations produced by Wako Pure Chemical Industries,Ltd., whose triglyceride contents were indicated to be 104 mg/dl and 280mg/dl, respectively. As a result, the triglyceride content of thesepreparations were found to be 104 mg/dl and 280 mg/dl, respectively.

On the other hand, the triglyceride content of the same controlled serumpreparations was determined by the method of saponification withpotassium hydroxide as described in Clin. Chim. Acta, Vol. 22, p. 393(1968). The measured values were 103 mg/dl and 279 mg/dl, respectively,being consistent with those obtained with the reagent containing the LPLaccording to the present invention.

In the triglyceride determination using the present reagent prepared byusing the LPL of the present invention, the time required for absorbanceto reach a constant level was about 8 minutes, whereas it was 23 minutesusing a reagent prepared by using the LPL of Pseudomonas origin(produced by TOYOBO Ltd.). Thus, the use of the LPL according to thepresent invention greatly reduces the time required for thedetermination of triglycerides.

Further, each of a reagent comprising the abovedescribed glycerol colorforming solution and 5 μl of the LPL obtained in Example 1 (8 U/ml) anda conventional reagent comprising the same glycerol color formingsolution and 5 μl of the LPL of Pseudomonas origin (product of TOYOBO,Ltd.) (8 U/ml) was allowed to stand at 25° C. for 4 days. Then, thetriglyceride content of the above-described control serum preparationswas determined with each of the thus preserved reagents. As a result,100% of the triglycerides were detected using the present reagent in 8minutes from the start of determination, while only 80% of thetriglycerides could be detected using the conventional reagent in 8minutes.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications ca be made therein withoutdeparting from the spirit and scope thereof.

We claim:
 1. A thermostable lipoprotein lipase capable of hydrolyzingtriglycerides in lipoproteins to glycerol and fatty acids, saidhydrolyzing activity being about 100% retained after treatment in abuffer having a pH of from about 4 to 7 at about 60° C. for about 15minutes,wherein said thermostable lipoprotein lipase has a glycerolforming activity and a fatty acid forming activity, such that saidglycerol forming activity is at least about 15% of said fatty acidforming activity; has a pH optimum of from about 8 to 9; has a stable pHof from about 4 to 7; and a temperature optimum of about 50° C. to 60°C.
 2. The thermostable lipoprotein lipase according to claim 1, whereinsaid thermostable lipoprotein lipase is obtained from Streptomyces 7825(FERM P-9983, FERM BP-2489).
 3. The thermostable lipoprotein lipase ofclaim 1, wherein said lipase has a molecular weight of about 30-50,000daltons by gel filtration and is inhibited by magnesium.